1. Field of the Invention
The present invention relates to equipment used in the manufacture of ophthalmic device molds, and, in particular, to equipment used in the manufacture of contact lens molds.
2. Description of Related Art
Soft hydrogel contact lenses have increased in popularity since they were first introduced in the 1970s. Such contact lenses are conventionally formed through a process in which the material used to make the lenses is placed between two halves of a casting mold, i.e., an anterior mold half and a posterior mold half. The mold halves are assembled to retain a volume of curable liquid, which is then cured to form the desired contact lens shape.
The anterior and posterior mold halves used to form the contact lenses are typically formed from polymers such as, for example, polystyrene or polypropylene, and are manufactured through a molding process. In forming the mold halves, molten polystyrene is typically provided, via an extrusion system, to a plurality of mold inserts in a mold forming apparatus. For example, a convex portion of a mold insert forms an optical quality surface on a concave surface of the anterior mold half. The concave optical surface of the anterior mold half can then be used to form the convex (anterior) optical surface of a contact lens. Similarly, a concave portion of an additional apparatus insert may form an optical quality surface on a convex surface of the posterior mold half. The convex optical surface of the posterior mold half can then be used to form the concave (posterior) optical surface of the contact lens.
As shown in U.S. Pat. No. 5,702,735 to Martin et al. (“the '735 patent”), an apparatus for manufacturing contact lens mold halves includes a number of mold cavities and a system for providing molten lens material to the cavities. The components of the apparatus that define the optical quality surfaces of the mold halves include a hollow cylindrical bushing and a removable insert mounted therein. In the manufacturing process, the insert is changed out so that the prescription strength of the contact lens formed by the resulting mold halves may be varied
Although the apparatus illustrated in the '735 patent may form contact lens mold halves, such an apparatus can be difficult and time consuming to use due to variations inherent to the molding process. For example, in order to manufacture contact lens mold halves of a desired radius, a matrix of step tools must be used to setup the apparatus. First, a nominal step tool is used to produce a batch of baseline molds. The baseline molds are measured for accuracy, and a series of step changes must then be made until the desired dimensions are achieved in the resulting mold halves. The apparatus must be shut down in order to change out the step tools, and multiple step changes are often required during setup. In addition, because each step tool includes an optical quality surface, the tools are very time consuming and expensive to produce.
Accordingly, the disclosed system and method are directed towards overcoming one or more of the problems set forth above.